SCHEME OF WORK
WEEK
|
TOPIC
|
1
|
Introduction/Scheme of work
|
2
|
Central Processing Unit (CPU)
·
The
CPU
·
Components
of the CPU
·
Functions
of:
·
Arithmetic
and Logic Unit (ALU)
·
Control
Unit (CU)
·
Register
|
3 – 4
|
Memory Unit
·
Computer
memory
·
Types
of memory
·
Description
of the types of memory
·
Unit
of storage
·
Conversion
from one unit of storage to another
|
5
|
Logic Circuits I
·
Definition
of Logic gate
·
Types
of logic gate and their description
·
Equation
and truth table for each logic gate
|
6-7
|
Logic circuits II
·
Types
of alternative logic gate
·
Description
of the alternative logic gate
·
Equation
and truth table for each alternative logic gate
·
Uses
of logic gate
|
8-9
|
Computer data conversion
·
Definition
of register, address and bus
·
Types
of registers and their functions
·
Fetch
– execute cycle
·
Factors
affecting speed of data transfer
|
10
|
REVISION
|
TOPIC ONE: THE CENTRAL PROCESSING UNIT
The Central Processing Unit (CPU) is the computer
component that's responsible for interpreting and executing most of the
commands from the computer's other hardware and software.
All sorts of devices use a CPU, including desktop,
laptop, tablet computers, and smartphones...even your flat-screen television
set.
Intel and AMD are the two most popular CPU manufacturers for
desktops, laptops, and servers, while NVIDIA
and Qualcomm are big smartphone and tablet CPU makers.
CPU has different names including processor,
microprocessor or the “brain of the computer”.
A modern CPU is usually small and square, with
short, rounded, metallic connectors on its underside. Some have pins instead of
metallic connectors.
The CPU attaches directly to a CPU ‘socket’ (or sometimes
a ‘slot’) on the motherboard. The CPU is inserted into the socket
pin-side-down.
The clock speed of a processor is the number of
instructions it can process in any given second, measured in hertz (Hz). A CPU
with a clock speed of 3.0 GHz can process 3 billion instructions each /per
second.
Some devices have a single-core processor while
others may have a dual-core (or quad-core, etc.) processor.
Components of the
CPU
The components of the CPU work together to achieve its
functions. The three components are:
1.
Arithmetic Logic Unit
2.
Control Unit
3.
Registers
Functions of Arithmetic
Logic Unit (ALU)
·
Executes all arithmetic operations such as ADD,
SUBTRACT, DIVIDE etc.
·
Executes logical operations (i.e. making comparison)
such as AND, OR, XOR etc.
Functions of Control
Unit (CU)
·
It directs the flow of data and information in the
computer.
·
It oversees the operation of the input and output
(I/O) devices.
·
Interprets instructions
Registers:
Register are temporary storage location used to quickly accept, store, and
transfer data and instructions that are being used immediately by the CPU. They
are special purpose memory which resides within the CPU.
TOPIC TWO: COMPUTER
MEMORY
Computer memory is the storage space in the computer
where the data to be processed and the instructions required for processing are
stored.
Types of memory
There are basically two major types of memory, which
includes:
·
Primary memory (main memory)
·
Secondary memory (external storage)
PRIMARY MEMORY
Also known as the main memory is the storage in the
computer in which data is stored for quick access by the CPU and are connected
via a memory bus. The primary memory is divided into two:
Random Access Memory (RAM)
The RAM is the volatile memory that temporarily
stores data and instruction currently being used by the computer. It is called
volatile because the content of it disappears when the computer is turned off
or there is loss of power supply.
Read Only Memory (ROM)
The ROM is the non-volatile memory that stores small
program that the computer can use to perform some of the basic operations
required to initiate the boot process. The content of the ROM are often times
stored by the manufacturer of the system and always permanent. Since the
content of it can only be read, they are called Read Only. Have you ever seen the black/blue background with some
information during the booting process? That’s the content of the ROM being
displayed.
SECONDARY MEMORY
This is the permanent, non-volatile memory that is
not directly accessed by the computer/processor. Before the content of the
secondary memory can be used by the computer, it must be copied into the RAM. It
has the capacity to store huge amount of data. The secondary storage is the slowest
and cheapest form of memory. Examples of secondary storage include Hard Disk
(Local Disk), Optical disk (CD, DVD), Floppy Disk, USB flash drive, memory card
etc.
Differences between primary and secondary memory
Primary
|
Secondary
|
It is the internal memory
|
It is the external memory
|
It is under the direct control of the CPU
|
It is not directly under the control of the CPU
|
It cannot be used for massive data storage
|
It can be used for massive data storage
|
It is faster than the secondary storage
|
It is slower than the primary storage
|
It does not supplement the secondary storage
|
It supplements the primary storage
|
Assignment 1:
1.
Write the difference(s) between CD-R and CD-RW,
DVD-R and DVD-RW
2.
Write the size, and technology of the following
storage devices:
·
Hard disk
·
Floppy disk
·
USB flash drive
·
Magnetic tape
·
Compact Disc
Unit of storage
The storage capacity is the amount of space
available for the storage of data in a particular storage media. The storage
unit includes:
·
Bits: a bit is a contraction of the word “binary
digit” and is denoted with either 1 or 0. A bit is the simplest unit of data
storage.
·
Nibble: a nibble is a collection of 4 bits
·
Byte: a byte is a collection of 8 bits
·
Word: a word is 2 bytes
·
Kilobyte: a kilobyte is 1024 bytes (1000 bytes
approximately)
·
Megabyte: a megabyte is 1048576 bytes i.e. 10242bytes
(1 million bytes approximately)
·
Gigabyte: a gigabyte is 1073741824bytes i.e. 10243bytes
(1 billion bytes approximately)
·
Terabyte: a terabyte is 1099511627776 bytes i.e.
10244bytes (1 trillion bytes approximately)
Conversion from one unit of storage to another
1.
Convert 64 bits to byte
Solution:
8 bits make 1 byte
1 bit makes 1/8 byte
64 bits make 1/8 x 64 = 8 bytes
2.
Convert 16384 bits to byte and kilobyte
Solution: a.
8 bits = 1 byte
1 bit = 1/8 byte
16384 bits = 1/8 x 16384
=
2048 bytes
b. 1024 bytes = 1 KB
1 byte = 1/1024 KB
2048 bytes = 1/1024 x
2048
= 2KB
Assignment 2:
a.
Explain the following units of storage
·
Petabyte
·
Zettabyte
·
Yottabyte
b.
Convert 0.5 Terabyte to megabyte
TOPIC THREE: LOGIC GATE
A logic gate is the fundamental building block of digital
integrated circuits. Most logic gate takes an input of two binary values, and
output a single value of 1 or 0. Some circuits may have only a few logic gates,
while others, such as microprocessors, may have millions of them. Logic gates
are primarily implemented using diodes or transistors acting as electronic
switches, but can also be constructed using vacuum tube, fluidic logic, optics,
molecules or even mechanical elements.
Logic circuit includes such devices as registers,
arithmetic logic units, and computer memory, all the way up through complete
microprocessors, which may contain more than 100 million gates.
Types of logic circuit
There are mainly 3 logic gates, they are:
·
OR gate
·
AND gate
·
NOT gate
1.
OR
gate: the OR gate is a circuit that has two or more inputs and
operates in such a way that:
·
Its output is 1 when any of the input variables is 1
·
Its output is 0 if when all of the input variables
are 0
·
Its output is 1 when all of the input variables are
0
The algebraic symbol of the OR operation is the plus
sign (+).
The OR gate is represented graphically below.
The OR is represented in the truth table below
A
|
B
|
X=A + B |
0
|
0
|
0
|
0
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
It can also be generated using the equation : X=A+B
2.
AND
gate: The AND gate is a circuit that has two or more inputs and
operates in such a way that:
·
Its output is 1 if and only if the two inputs are 1
·
Its output is 0 if any of the inputs is either 0 or
1 or both are 0
The algebraic symbol of the AND gate is * or .. The AND gate is represented graphically below.
3.
NOT
gate: This is the logic gate that has one input and one output such
that when the input is true (1), the output is false and when the input is
false, the output is true.
Equation and truth table
for each logic gate
The truth table is the table that shows the possible
combinations of variable values in the equation and the result (output) for
each of the logic gates.
For a two-input truth table, there will be 4 (22) possible combinations
of variable inputs and generally for n-input
truth table, there will be 2n possible combinations of the input
variables. See the examples below:
1.
OR
gate: The algebraic equation (with two inputs A and B): x = A+B , is represented in the truth
table below
A
|
B
|
X = A+B
|
0
|
0
|
0
|
0
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
Check the rules under the OR gate.
2.
AND
gate: The algebraic equation(with two inputs A and B) : x = A.B, is represented in the table
below
A
|
B
|
X = A.B
|
0
|
0
|
0
|
0
|
1
|
0
|
1
|
0
|
0
|
1
|
1
|
1
|
Check the rules under the AND gate.
3.
NOT
gate: the truth table for the NOT gate (with input A): x= A’ or x= á¾¹ is shown
below
A
|
X = á¾¹
|
0
|
1
|
1
|
0
|
Assignment 3: An OR gate has 3 inputs and 1 output.
Show the truth table for this OR gate.
TOPIC FOUR: LOGIC GATES II
1.
NAND
GATE
This is a logic gate whose output is zero (0) if both of the inputs are 1and
1 otherwise. A NAND gate is equivalent to an AND gate followed by a NOT gate.
The NAND gate is the complement of the AND function. The word NAND is got from
the abbreviation NOT-AND. The NAND gate is represented graphically below.
The truth table is shown below
Construction of a simple comparator using XOR
A comparator is a circuit that compares two input
voltages and indicates which is higher. One of the special logic circuit that
occurs quite often in digital system is the exclusive-OR (XOR) circuits.
The XOR produces a high voltage when the two inputs
are at opposite levels. This means that the XOR yields true (1) if and only if
one of the inputs is true (1) and the other is false (0). The XOR gate is
graphically represented below.
The XOR is represented in the truth table below
TOPIC
FIVE: COMPUTER DATA CONVERSION
Register: the term register can be defined as a high-speed
storage location in the Central Processing Unit (CPU), which is used to hold
data and addresses to be processed by the computer. A register may hold a
computer instruction, a storage address or any kind of data. A register must be
large enough to hold an instruction. For example, in a 32-bit instruction
computer, the register must be 32-bit wide.
Address: an address is a name, label or number that identifies
a location where data or information is stored within the computer memory. It
is a particular location holding a word or a byte. Computer memory is an array
of storage boxes; each of these storage boxes is one byte in length. Each box
has an address (a unique number) to it.
Bus: In digital computing, a bus is a set of physical
connections (cables, printed circuits etc.), which can be shared by multiple
hardware components in order to communicate with one another. It is a
transmission path on which signals are dropped off or picked up at every device
attached to the line.
The purpose of buses is to reduce the number of
PATHWAYS needed for communication between the components by carrying out all
communication over a single data channel.
There are generally two types of buses:
Internal (System) bus: the internal bus enables communication between internal
components such as the memory and the video card. It connects the CPU to the
main memory. It is also called Front Side Bus (FSB) or memory bus.
External/expansion bus: this bus is capable of communicating with the
external components or peripheral devices. These devices connect to the
internal bus via a bridge implemented in the processor chipset. It is also
called input/output bus.
The
lines or pins of a bus are of three types:
Address
- the components pass memory addresses to one another over the address bus.
Control
- used to send out signals to coordinate and manage the activities of the
motherboard components.
Data -
transferred between peripherals, memory and the CPU. Obviously, the data bus
can be a very busy pathway.
Types of registers and their functions
Memory Data Register (MDR)
This is the register that contains the data to be stored in the computer memory
or the data fetched from memory and ready
to be processed by the CPU. It acts like a buffer and holds anything that
is copied from the memory ready for the processor to use it.
Current Instruction Register (CIR)
This is part of the CPU’s control unit that stores the instruction currently being
executed or decoded.
Memory Address Register (MAR)
This is the CPU register that either stores the memory address from which data
will be fetched to the CPU or the address to which data will be sent and
stored.
In other words, MAR holds the memory location of the
data that need to be accessed. When reading from memory, data addressed by MAR
are fed into the MDR and then used by the CPU. When writing to memory, the CPU
writes data from MDR to the memory location whose address is stored in MAR.
Difference between register and main memory
Register
|
Main
memory
|
Registers are internal, i.e. they are located
inside the processor
|
Main memory is external, i.e. it is located
outside the processor
|
They are very fast
|
It is slow
|
FETCH-EXECUTE CYCLE
Most modern processors work on the FETCH-EXECUTE principle.
It is based on the Von Newman Architecture. When a set of instructions is to be executed,
the instructions and data are loaded in main memory. The address of the first instruction
is copied into the program counter. The execution of an instruction by a
processor is divided in three parts. These parts are fetching, decode and
execute.
Fetch the next instruction
The program counter (PC) contains the address of the
next instruction to be executed, so the control unit goes to the address in
memory specified in the PC, makes a copy of the contents and places the copy in
the Current Instruction Register (CIR).
Decode the instruction
The next step is for the CPU to interpret the
instruction that has just been fetched and stored in the CIR. The CPU is designed to understand specific
set of commands called “instruction set” of the CPU. Each make of CPU has a
different instruction set.
The CPU decodes the instruction and prepares various
areas within the chip in readiness of the next step.
Get
data if needed
It may be that the instruction to be executed
requires additional memory accesses in order to complete its task. For example,
if the instruction says to add the content of the memory to a register, the
control unit must get the content of the memory location.
Execute
the instruction
Once an instruction has been decoded and any data
fetched, the control unit is ready to execute the instruction. If the
instruction involves arithmetic operation or involves comparison, the ALU is
called upon to handle this and send the result to a special register
(Accumulator) before being moved to the memory.
The control unit increment the value in the program
counter by 1 and the cycle begins again.
Factors affecting speed of data transfer
Bus speed: The term "bus speed" refers to how
quickly the system bus can move data from one computer component to the other.
The faster the bus, the more data it can move within a given amount of time.
It is measured in Hertz.
Bus width: The size of a bus, known as its width, is important
because it determines how much data can be transmitted at one time. For
example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit
32 bits of data.
